Electric initiator



3,04 ,223; a ELECTRICINITIATOR were-ans. clerk; Henna-o Coun y; Va., assigno to Texaco Experiment Incorporated, a corporation of Virginia v Filed Nov: 20, 1959, Set. No; 854,473 3 Claimsc (Cl. 102-702) Thisinvention relates to improvements in electric firing initiating devices and, more particularly, to electric initiators which are highly resistant to premature firing by radio frequency radiations.

The invention relates to electric firing initiating devices which generally/include a shell or casing in which is dis posed an electrical resistance-heater element or fuse'wire which heater element or fuse wire in in contact with a heat sensitive ignition composition or matchhead which, intum, is' emb'eddedin or located adjacent to an explosive charge,v

Suchelectrical firing initiating devices are commonly employed '--to initiate various explosive-compositionsused as the primary igniter for reaction propelledmoto rsof theliquid or solid propellant types.- In general, such electric initiatorsare designed to be actuated bydirect ourrent-or low frequency alternating current; The art has long recognized the dangers inherent in accidental discharge of electric initiators by accidentally induced radio frequency currents. However, the problem has' become more-acute'in' recently years since radio frequency initiated guiding systems and control means have been employed in reaction propelled space vehicles;

It is, therefore, a primaryobject of'the present inventionto provide a direct current'or low frequency alternating current electric initiator safeguarded-against pretriature or accidental initiation by radio frequency currents inducted therein.

A further object is to provide an improved radio frequency protected electric initiator without substantially reducing the degree of sensitivity of the electric initiator to'direct' or low frequencycurrent;

Other objects and advantages of the-invention will become apparent to those skilled in the art from the following description with reference tothe accompanying dra'wings wherein:

FIG. 1 is an enlarged vertical sectional view of an electric initiator embodying the principles of the present invention;

FIG. 2 is a top plan view of the initiator shown in FIG. 1;

FIG. 3 is a sectional view of the pairs of conductors substantially on line 3-3 of FIG. 1; and

FIG. 4 is an enlarged diagrammatic view of the condoctors and fuse wire shown in FIG. 1 illustrating the cross connection of the conductors to the ends of the fuse Wire.

In general, the electric initiator safeguarded against premature initiation from high frequency currents induced therein comprises a casing having a heat-sensitive ignition composition therein, an electrical resistance heater ele ment in heat exchange relationship to the ignition composition, a first pair of electrical conductors in close proximity to each other terminating at one end externally of said casing and cross-connected to said resistance element at the other end, a second pair of electrical conductors in close proximity to each other and to said first pair of conductors, said second pair of electrical conductors terminating at one end externally of said casing and crossconnected to said resistance element at the other end, and dielectric means insulating the conductors of the pairs of conductors from one another.

Referring to the drawings, represents a metal or the like casing of electric initiator 12. The casing 10 may be 3,43,223 Fatenteel July 10; 1962 2 7 provided on' its external surface with a bright silver coating to reduce the passageof radio frequency currents to the interior of the electric initiator 12.

Within the casing 12, a charge of explosive material 14 of the heat sensitivetype is maintained; Inheat exchange relationship to theignition composition 14is an electrical resistance heater element or fuse wire 16. Also, as illustrated in FIG. 1, theelectric initiator may include a small matchhead or primer spot 17' of a heat-sensitive explosive material, such as mercury fulminate-or the like, to aid in the initiation of explosion in the explosive charge 14.

The ends 18 and 20 of the electrical resistance heater element 16 are connected, as to be more fully described, to pairs of electrical conductors generally designated 22 and 24. The electrical conductors 22' include electrical conductive elements 26 and 28 maintained in close but insulated relationship to each other by,-for'example, dielectric insulating coatings 39.

The pair of conductive elements 26 and 28 should be; as close as possible, of the same length and preferably the conductors are maintained as close as possible to the center of the container 10 to reduce inductance of radio frequency energy from the wall of the container. The internal end of electrical conductive element 26 is connected to end 20of fuse wire 16 while the extended end of electrical conductive element Z8 -is electrically connected'to the opposite end 18 of rusewire 16 The assembly also'includes, as hereinbefore described, a second pair of electrical conductors generally designated 24.- The electrical conductors 24 include electrical conductive elements 34 and 36 maintained in close insulated relationship by insulating coatings 30, Conductor pair 24 is led-substantially concentrically into the casing 10 and to the fuse wire 16 in close proximity to conductor-pair 22. The inner end of conductive element 344's connected to end '20 of electrical resistance element 16 while electrical conductive element 36 is connected to the opposite end 18of electrical resistance element 16.

In order "to maintain all four conductive elements in close proximity to each' other throughout their passage centrally of the container 10, ariouter layer of dielectric material, illustrated at 32in FIGS. 1 and 3, may be used to surroundth'e twopairs of conductors.

Thus, it will be seen that one Wire of each pair of conductors 22 and 24 is connected to one of the ends 18 or 20 of the electrical resistance heater element 16 and the other Wire of each pair of conductors is connected to the opposite end of the heater element 16. By maintaining the wires of conductors 22 and 24 in closely spaced relationship if radiation is picked up by the electrical conductors, the current generated therein will be substantially the same in each element of a pair of conductors and will be applied to the fuse Wire 16 in opposite directions simultaneously causing cancellation of the generated currents, thus preventing heating of the fuse wire and premature unintentional ignition of the igniter.

It will also be appreciated by those skilled in the art that by placing the four conductors together in a group, the group presents the maximum symmetry to an electromagnetic Wave, and particularly Waves of very short Wavelengths. The closer together and smaller the conductors can be made, that is, the more nearly they appear as a single conductor, the higher will be the frequency against which they will protect.

Also, the central location of the two pairs of conductors provides a symmetrical capacitive eifect between all of the conductors and the case,

In order to ignite the ignition means, heater voltage is applied to the conductive elements of a pair of conductors 22 or 24 or the initiating current may be conducted to the fuse wire through conductive elements 26 and 36 or 3 28 and 34, thereby completing an electrical circuit through the electrical resistance heater element 16.

In order to maintain the protective feature of the initiatorof the invention, the selected conductive elements should not be etxernally attached to lead in conductors except at the moment of firing by means of a relay or the like.

A suitable firing system is illustrated in FIGS. 1 and 2 and comprises an electrical relay means 40 having a pair of spaced resilient conductive armatures 42 and 44 and a solenoid 46.

The initiating current, from a source not shown, is conducted to the solenoid 46 by conductors 48 and 50. Conductor 48 connects conductor 48 to armature 44 and conductor 50 connects conductor 50 to armature 42. The connection between conductor 48' and armature 44 and conductor 50' and armature 42 may be, as illustrated in the drawing, through insulated armature mounts 52.

The extended ends of the pair of armatures 42 and 44 are provided with contacts 54 which engage a pair of the contacts 56 when the solenoid 46 is energized.

It will be particularly noted that while only a pair of conductors are required for heating the fuse wire 16, all four conductors are provided with-contacts 56 in order to maintain symmetry and equal conductor lengths,

From the foregoing description, it will be seen by those skilled in the art that the present invention provides a very simple but highly effective means for safeguarding electric initiators against premature initiation from high frequency currents induced in the lead wires thereof. It will also be apparent to those skilled in the art that various modifications may be made in the form of the device with out departing from the scope of the present invention. For example, in the illustrated form of the invention, the conductive elements of each pair of conductors are shown as being straight and parallel to each other. However, as an alternative form, the conductive elements of the pairs of conductors may be twisted around each other and then provided with the protective outer insulating coating 32.

I claim:

1. An electric initiator safeguarded against premature initiation from high frequency current induced therein comprising a casing having a heat-sensitive ignition composition therein, an electrical resistance heater element in heat exchange relationship to the ignition composition, a first pair of electrical conductors inclose proximity to 4 each other terminating at one end externally of said casing and cross-connected to the ends of said resistance element at the other end, a second pair of electrical conductors in close proximity to each other and to said first pair of conductors, said second pair of conductors terminating at one end externally of said casing and crossconnected to the ends of said resistance element at the other end, each of the conductors of said first and second pairs of conductors being of substantially the same length, and dielectric means insulating the conductors of the pairs of conductors from each other.

2. The invention defined in claim 1 wherein said first and second pair of electrical conductors extend centrally throughout a substantial portion of the length of said casing.

3. An electric initiator safeguarded against premature initiation from high frequency currents induced therein comprising a casing having a hCatrSEHSitiVB ignition composition therein, an electrical resistance heater element in heat exchange relationship to the ignition composition, a first pair of electrical conductors in close proximity to each other terminating at one end externally of said casing and cross-connected to opposite ends of said resistance element at the other end, each of the electrical conductors of said first pair of electrical conductors being of substantially the same length, a second pair of electrical con ductors in close proximity to each other and to said first pair of conductors, said second pair of conductors terminating at one end externally of said casing and crossconnec-ted to opposite ends of said resistance element at the other end, each of said conductors of said second pair of electrical conductors being of susbtantially the same length as the first pair of conductors, dielectric means insulating the conductors of the pairs of conductorsirom each other and switch means for selectively connecting at least two of the electrical conductors connected to opposite ends of said resistance element to a source of firing initiating current.

References Cited in the file of this patent UNITED STATES PATENTS 1,094,692 Allison Apr. 28, 1914 2,389,086 Stuart Nov. 13, 1945 FOREIGN PATENTS 1,143,929 France Oct. 7, 1957 

